1. Field of the Invention
The present invention is directed to an anchor for use in a friable substrate, particularly to a self-drilling anchor for use in drywall.
2. Description of the Related Art
Because drywall is a friable substrate, mounting articles thereto can be difficult. In the past, high-threaded self-drilling anchors have been used, such as those sold under the trademark E-Z ANCOR by ITW Buildex and disclosed in the commonly assigned U.S. Pat. No. 4,601,625. However, typical self-drilling anchors usually can hold only objects of light to moderate weight. In order to increase the load capacity of a self-drilling anchor, it was typically necessary to increase the diameter of the anchor, which increased the possibility of damage to drywall and left a large, unsightly hole in the drywall.
For heavier loads, toggle bolts and nylon toggles have been used. However, toggle bolts typically require a separate pre-drilling step and are usually expensive, complicated to install, and unreliable because a user typically has to undergo a difficult sequence of assembly to put together and install the toggle bolt. Nylon toggles are also unreliable and typically are only designed for predetermined drywall thicknesses.
Attempts have been made to improve pullout resistance without the increased expense and unreliability of toggle bolts. The anchor disclosed in U.S. Pat. No. 6,676,348 to Hoppe includes expandable tongues which help fasten the anchor in a substrate. However, the anchor of this patent requires a user to pre-drill a hole in the substrate. Moreover, the anchor does not include threading for engaging the substrate.
The self-drilling anchors disclosed in U.S. Pat. Nos. 6,186,716 and 6,354,779 to West et al. have a part that is pivoted into the drywall by a mounting fastener. While these anchors typically provide increased pullout resistance over typical self-drilling anchors, they usually do not provide enough anchor expansion to hold heavy objects.
Some self-drilling drywall anchors include portions that expand behind the drywall in an attempt to increase pullout resistance, such as the anchor sold under the trademark WALLGRIPPER by Cobra Anchors. However, anchors such as these are difficult for a user to get to function properly and may provide different results for different drywall thicknesses.
What is needed is an anchor for a friable substrate that may be easily installed and provides high pullout resistance and load capacity for heavy loads.